1. Field of the Invention
This invention relates to an image sensing apparatus having a follow-up type color balance adjusting function whereby a color balance control condition is adjusted following changes in the color component ratio of the external light and a setting type color balance adjusting function whereby the color balance adjustment is controlled according to a preset state obtained by presetting a color balance control condition.
2. Description of the Prior Art
The basic operations of the television cameras includes a color balance adjusting operation called white balancing. This operation is arranged to control the red (R), green (G) and blue (B) color signals included in an image pick-up signal representing a white object to bring them into a ratio of 1:1:1 to each other. Theoretically, the white balance can be obtained by photographing a white object and by adjusting the gains of red (R) and blue (B) signals during a color system processing operation to bring, for example, each of the two color difference signals R-Y and B-Y of red and blue systems to a zero level. Heretofore, varied kinds of automatic white balance adjustment devices which automatically perform white balance adjustment have been proposed for house hold or industrial television cameras, because these cameras must meet the following requirements.
1. The operation by the operator on the device is either simple or not required at all. PA0 2. No great image deterioration results from an error in the operation on inadvertent ommission of the operation. PA0 3. White balance must be adequately attained even under the conditions 1 and 2 above. PA0 (1) Follow-up type white balance adjusting function White balance is adjusted by utilizing the color component ratio within the external light in addition to the photo-taking light of the television camera. This normally requires no operation by the photographer. PA0 (2) Setting type white balance adjusting function: White balance is adjusted according to the chrominance signal ratio in the image pick-up signal of the television camera. This function is generally performed while a switch is pushed by the photographer. PA0 (a) Setting at a suitable preset value when a power supply is switched on. PA0 (b) Holding the preset value even after the power supply is switched off.
To meet these requirements, there have been proposed automatic white balance adjusting functions which can be classified roughly into the following two types:
The follow-up type white balance adjusting function mentioned in paragraph (1) above is performed by an open-loop control system controlling an image pick-up signal on the basis of information other than the image pick-up signal. In order to attain sufficiently accurate white balance adjustment by this system, the degree of error of each part of the system must be minimized. This requirement for increased precision of each part then results in a complex system arrangement. This is a drawback of the follow-up type function.
In the case of the setting type white balance adjusting function, the levels of the color difference signals R-Y and B-Y are set by feedback control to become a zero level respectively. They are then arranged to be kept in that state in a digital or analog manner. In other words, the setting type function is performed by a closed loop control system. Even if there is some error element within the system, white balance is accurately adjustable so long as the system is stable in terms of aging and temperature. However, the setting type system necessitates a manual pushing operation on a setting switch for picking up an image of a white object. In this case, while the white balance adjusting accuracy after the setting operation is ensured as mentioned above, the system does not ensure the accuracy before setting. To solve this problem, the following contrivances have been attempted:
However, such arrangement still does not sufficiently ensure accurate white balance adjustment against the above-stated inadvertent omission of the setting operation.